C. F. ROUSSELET ON BRACHIONUS BAKERI. 331 



specimen in my bottles, but fortunately Dr. Measures, who had 

 collected at the same spot, had obtained a number of specimens 

 showing in varying degrees indications of posterior spines. 

 Fig. 14 represents one of these animals, possessing the longest 

 spines found in this gathering, but every degree between this 

 and no spines at all is represented ; in some specimens even 

 the shell has a very short spine on one, the left, side, and is 

 rounded off on the other as represented in Fig. 13. 



The mental edge of B. baheri is a wavy line as seen in Fig. 3, 

 showing three rounded elevations. and three depressions on each 

 side, with a deeper depression in the centre, but the exact out- 

 line of the margin varies somewhat. . 



One of the functions of spines in the Rotifera is protective. 

 Animals having long spines cannot be so easily swallowed by 

 aquatic larvae, worms, and the larger Rotifers, such as As- 

 planchna?. I have often observed how the spines have saved its 

 possessor from such an awful fate. It is, however, not easy to 

 conceive what can be the factors at work to produce so much 

 variety in the size and shape of the spines in the same species. 

 No doubt food supply, climate, environments, and consti- 

 tution of the water are some of the factors of variation, but 

 what conditions in the environments or exact composition of the 

 water will produce, for instance, long spines, it is at present 

 impossible to say. Certain it is that all these varieties are 

 never found together ; as a rule each locality has one or two 

 varieties which may be very abundant for a time and then dis- 

 appear altogether ; after a time the same variety may reappear, 

 or it may be replaced by a different variety. 



The males of the different varieties cannot, I think, be dis- 

 tinguished from each other; I have mounted specimens of 

 some of them. They have all a very thin spineless lorica as 

 figured by Mr. Gosse. 



The following older species I consider to be varieties of 

 B. bakeri : — 



Brachionus brevispinus, Ehrbg. 



„ polyceros, Schmarda. 



.,, a,7icylognathus, Schmarda. 



,, chiliensis, . ■ ,, 



,, pustulatus, ,, 



and of the more recently described species the following will 



